RF coverage and interference planning - WorldDAB

RF coverage and interference planning

WorldDAB and ABU DAB+ technical webinar series

Dr. Les SabelS-Comm Technologies and WorldDAB Technical Committee

RF Coverage and interference

Coverage requirements

Field strength reference levels

Transmission network considerations

SFN design and performance

Planning and Interference

Case study

Requirements

High level requirementsCoverage areas are usually defined by the country’s

Broadcasting Regulator• Wide area broad targets e.g. 90% of country area or

95% of country population• Specific coverage requirements

– Licence Area Plans (LAPs)– Cities, towns, roads– Radio station target audience

• Coverage is often planned to be implemented in phases – usually the highest population areas first

UK channel allotments

Requirements

Capacity

How many services both now and later will be required in each area• Defines how much spectrum is needed• E.g. Sydney uses 3 ensembles (5.136MHz) for approx 63 services

Typically dimensioned for 64 kbps per service including PAD

Requirements

Spectrum

How much of VHF Band III is available?

Cross border coordination impact

Spectrum reuse, typical cellular design requires 3-5 times single cell capacity dependant on terrain and coverage requirements

2 DTV channels allocated14MHz = 8 DAB channels = 8A, B, C, D, 9A, B, C, D

Requirements

Germany

Full VHF Band III

MFN and SFN

SFNs are usually contained within a larger MFN structure

Still requires frequency coordination with neighbouring countries

National SFN Sub-National SFNs MFN


Coverage TargetsReception modes from vehicle to urban


Coverage Targets

Minimum field strength for each reception mode depends on many variables• Location variation• Man Made Noise• Antenna gain• Receiver performance / Noise Figure• Building entry loss

– Building types and density have significant impact– Ground level vs high levels, opposite side of building

• Cars generally OK if in-building performance is satisfactory



Planning field strengths summaryRx height = 1.5m

Planning field strengths (dBμV/m)

Mobile

outdoor

Sub

Urban

Urban Dense

Urban

Australian planning field strength 50 54 60 70

EBU Tech 3391 planning field strength 42.8 43 65.7

:

Differences mainly due to assigned antenna gain and MMN level

Tech 3391 is for Portable Outdoor rather than Suburban Indoor

Building entry loss adds over 10.5 dB

Unofficial – for reference purposes only


High Power High Tower (HPHT) v Low Power Low Tower selections (LPLT)

• Higher sites will always provide greater coverage due to increased line-of-sight areas

• Terrain is the largest impact on coverage area, large buildings are equivalent to hills!

• Uneven and shadowed terrain requires increased main site power and/or increased repeaters

Type Power (kW ERP)

Typical height above served area (m)

Best use

HPHT 10 - 50+ >100 wide area coverage but may experience shadowed areas especially in the distant coverage areas

MPMT 2 - 10 30-100 undulating areas with no high transmission site

LPLT 0.1 - 2 <30 local area coverage

Transmission network considerationsHPHT – LPLT Cost implications

• HPHT are generally preferred for wide area coverage

• will usually give best coverage kms2/$

• Repeater sites are often LPLT to cover specific areas

• City sites can be very expensive, even for LPLT• High population density drives prices up even for sites like water towers• Telco towers are often too low!

• Site costs are often the largest component of Opex for main AND repeaters

• Site selection for cost optimisation is time consuming – especially for multiple repeater sites in large cities

• The number of main HPHT sites in large cities are often limited

Multi-Frequency Networks (MFN) and Single Frequency Networks (SFN)


MFNMultiple different multiplexes

SFNMain Tx and 2 Gap Fillers

All transmitters must deliver the same content to the area concerned

All transmitters can deliver different content to the area concerned


Covering a specific area, e.g. a Licence AreaHigh spectral efficiency

Commercial licence areas - Northern NSW example

Each licence area has its own local content and SFN to ensure appropriate coverage


The DAB SFN model

ETS 300 799

Single Frequency Networks

GPS 1PPS

GPS 1PPS

GPS 1PPS

The transmission launch time is controlled by the TImeSTamp (TIST) parameter in the ETI stream.

All transmitters in an SFN must be time aligned

The multiplex embeds a TIST time stamp in each ETI frame which defines the time it is assembled relative to a coordinated timing reference, e.g. 1PPS

All transmitters are required to be aligned to a 1PPS timing signal derived from GPS/Glonass

Some adjustment of the maximum operating distance and hence the area which may experience interference can be made using the transmission delay of individual transmitters

SFN timing

The DAB signal is designed to allow SFN operation over a distance of 73.8 km

• Guard Interval Δ for Mode 1 = 246 µS

• SFN distance limit = c Δ = 73.8 km

• Performance impact of out of GI

• See EBU Tech 3391

SFN timing constraints

Protection ratio for out of GI transmission components

Interference

OK

Tx 2

-12 dB

Tx 1

246 µS

The standard terminology for the delays in the systems are shown below

NOTE that transmitter manufacturers sometimes use their own terminology

Timing model

See ETSI ETS 300 799 – annex F

Link Fed Repeater

Repeater types – link fed

The repeater is fed by an EDI / ETI signal via a link- Microwave- Telco landline (fibre, dedicated or shared, diversity)

Telco Link

Microwave link

On Channel Repeater

Repeater types – on-channel

Receives the signal off-air and then retransmits on the same frequencyEcho cancelling techniques allow repeaters which can re-transmit on the same frequency The maximum power of the OCR is dependent on - the input signal power after Rx antenna gain - The Tx antenna to Rx antenna coupling ratio – Rx and Tx nulls provide most attenuation- The accuracy of the echo cancelling system – typically 10dB of local signal can be

cancelled

Main transmitter input signal

Feedback from repeater output antenna to OCR input antenna

OCRs are low power e.g. <1 kW

Only issues if

- field strength difference is < CCI PR (12dB)

- time of arrival difference (ToA) is > GI (246 uS)

Examples - OCR

𝑇𝑇𝑇𝑇𝑇𝑇 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 = 𝑇𝑇𝐴𝐴𝐴𝐴 𝑂𝑂𝑂𝑂𝑂𝑂 𝑡𝑡𝑑𝑑𝑡𝑡𝑑𝑑 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 − 𝑀𝑀𝑑𝑑𝑑𝑑𝑑𝑑 𝑡𝑡𝑑𝑑𝑡𝑡𝑑𝑑 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 µ𝐴𝐴

𝑇𝑇𝑇𝑇𝑇𝑇 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 = 𝑇𝑇𝐴𝐴𝐴𝐴 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑀𝑀𝑑𝑑𝑑𝑑𝑑𝑑 𝑑𝑑𝑡𝑡 𝑂𝑂𝑂𝑂𝑂𝑂𝑑𝑑

+ 𝑂𝑂𝑂𝑂𝑂𝑂 𝑝𝑝𝑑𝑑𝑇𝑇𝑑𝑑𝑑𝑑𝑝𝑝𝑝𝑝𝑑𝑑𝑑𝑑𝑝𝑝 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 + 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑂𝑂𝑂𝑂𝑂𝑂 𝑑𝑑𝑡𝑡 𝑂𝑂𝑅𝑅𝑑𝑑

− 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑀𝑀𝑑𝑑𝑑𝑑𝑑𝑑 𝑑𝑑𝑡𝑡 𝑂𝑂𝑅𝑅𝑑𝑑

µ𝐴𝐴

CCI issues only possible if the OCR is > 34 km from the main Tx

The example model uses Egli’s Rayleigh channel model for field strength prediction with exponent 3.8

Edge of coverage extension

Examples - OCR

70 km

50 kW 1 kW

246 µS

The time delay of the OCR signal must take into account the time required to travel to the OCR site and the OCR processing delay

Zone of potential interference

Edge of coverage extension

Examples - OCR

70 km

50 kW 1 kW

Impact of shadowing of main signal by high object

Shadow loss of 20 dB causes main signal to weaken below the CCI PR limit = coverage hole

OCRs are useful but care is needed to ensure no unexpected holes in coverage

Shadow zone

LFRs can be various powers from small infill at 1 kW to full main power

Only potential issues if the transmitter site spacing is >73.8 km

Issues only usually occur in shadowed areas

Examples LFR

𝑇𝑇𝑇𝑇𝑇𝑇 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 = 𝑇𝑇𝐴𝐴𝐴𝐴 𝐿𝐿𝐿𝐿𝑂𝑂 𝑡𝑡𝑑𝑑𝑡𝑡𝑑𝑑 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 −𝑀𝑀𝑑𝑑𝑑𝑑𝑑𝑑 𝑡𝑡𝑑𝑑𝑡𝑡𝑑𝑑 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 µ𝐴𝐴

𝑇𝑇𝑇𝑇𝑇𝑇 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 = 𝑇𝑇𝐴𝐴𝐴𝐴 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝐿𝐿𝐿𝐿𝑂𝑂 𝑑𝑑𝑡𝑡 𝑂𝑂𝑅𝑅𝑑𝑑

− 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑀𝑀𝑑𝑑𝑑𝑑𝑑𝑑 𝑑𝑑𝑡𝑡 𝑂𝑂𝑅𝑅𝑑𝑑

µ𝐴𝐴

Wide area coverage

No shadowing

Examples - LFR

130 km

50 kW 10 kW

Wide area coverage

With shadowing loss (10dB)

Examples - LFR

130 km

50 kW 10 kWShadow zone

246 µSZone of potential interference

246 µS

Co-Channel Interference

Planning and interference

The Co-Channel Interference allowance defines the minimum distance between different transmissions on the same frequency block

What is the maximum allowable interference field strength?

The maximum interfering field strength is defined relative to the wanted field strength• the Co-Channel Protection Ratio typically 12 dB.Terrain between co-channelled areas strongly influences the level of interference

Unwanted interfering DAB service

Wanted DAB serviceMinimum

54 dBuV/m

A B

Planning and interference

Allotment planning• Determines the frequency blocks to be used in each area with individual content• The CCI between areas using the same frequency block is usually required to be less

than a specific measurement value, e.g. less than 2% of the interfered areas population

Cross border planning and coordination• usually done using the ITU P.1546 propagation model• includes all users of VHF Band III – DAB and DTT

Sydney, Australia

Case Study

Single 45 kW main transmission

30 km

Areas more than approx. 30 km west of the main transmitter only receive vehicle grade coverage

> 80 dBµV/m – dense urban indoor

> 60 dBµV/m – urban indoor

> 54 dBµV/m – suburban indoor

> 50 dBµV/m – vehicle

Field strength pallete

Sydney, Australia

Case Study

5 repeaters

52 km

2 x LFR @ 500W

3 x OCR @ 300W

Largely cover the populated areas with at least suburban grade coverage

Further urban expansion in Western Sydney will require further repeater support for indoor coverage

Case study

Sydney northern beaches - Terrain shielding and undulations

Case study

With 300W repeater

Case study

City building shielding - Melbourne

Mt Dandenong transmitter 45kms

SFN coverage in Sale, Victoria, Australia

Case study

7 transmitters to cover 200km ranging from 1 to 5kW each

Conclusions

1. Coverage requirements come first BUT may need to be adjusted depending on the demand for and availability of spectrum

2. Full coverage can be provided BUT there will always be a trade-off between % coverage and COST

3. The last few % of population coverage can be very expensive – needs to be realistic

4. Generally better to plan the overall national network allotments and then rollout the infrastructure in phases

5. Always use SFNs to advantage to maximise spectral efficiency6. Use modern coverage planning and interference analysis tools to maximise

accuracy – good planning can save SIGNIFICANT cost

7. Plan ahead within an overall programme of activities to establish DAB+

Thank you

For further information, please contact:www.worlddab.org

or [email protected]

http://www.worlddab.org/

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RF coverage and interference planning - WorldDAB